I've been collecting NOS and good used parts for some time. I'm ready to start assembling one of my BS90 premix engines. This will be my first engine assembly of any kind. I've been studying the parts/tech manuals and I'm very familiar with them. I have NOS gaskets/packing, seals, o-rings, bearings, piston and rings. I've cleaned all the original/used parts and engine cases. Now what? The manuals assume you already know these BASIC procedures. I can follow the assembly steps in the manual. I understand all the moving parts need to be well oiled. I also found member "reeds" recommend seal and o-ring grease. http://bridgestonemotorcycleparts.com/index.php?topic=3029.0What about the gaskets/packing?How about the head gasket?Do I need thread locker or anti-seize anywhere? If so, where, when, why and what type?Any other basic tips for first timers would be appreciated! Thanks, Steve

Hi Steve, Not many takers for this one, I guess most people who have reassembled vertically split engines could write a book on it and will have their own way of doing things but I will see if I can get the ball rolling. I'm not personally familiar with the 90 engine but I have rebuilt vertical splits before. Scariest part is getting all the parts in place and bolting up the crankcases, after that should be plain sailing using the manual. The 90 manual dismantling instructions do show a good logical sequence and will provide a helpful guide to putting everything back in its right place (mantled ) when reversed.

Any new bearings/seals should be pressed into the cases where appropriate. Lightly oil the bearing/seal outer and case recess. Apply pressure to the bearing outer race only and make sure they are started squarely. Support the case under the bearing housing. If the bearing stayed on the shaft when the engine was split, leave it in place. Using the parts manual, make sure all the case dowel pins are in place. Try a dry fit of the two case halves at this stage to see how easily they go together and separate again.

Lay out all the parts that go into the cases where you can see them, crank, gear box shafts, shift drum, kick start etc so nothing gets forgotten. Use the parts manual to check that all end shims and/or thrust washers, spacers etc are in place on the shafts. These are easily misplaced during cleaning or storage.

Support the right crankcase on wooden blocks and insert shafts in reverse order of removal as per manual. Looks like the gearbox shafts and shift drum go in as a cluster and is probably easier said than done, possibly needing an extra pair of hands. Might be easier to swing the case up vertical and slide the unit in horizontally so no bits fall off the shafts. I’m not sure how the kickstart spring is pretensioned on the 90, maybe someone could come in on that.

Once you’re happy all the parts are in place and everything will spin nicely, try another dry fit of the left case, might have to line up some of the shafts manually if they don’t automatically line up on the bearing holes. Gently press the halves together by hand, keeping them parallel with only light taps from a rubber mallet if needed. You should be able to get them to about half an inch apart when the bearings will start to seat on their shafts or press into the casing, stop at this stage. If at any time you feel hard resistance to the cases closing, stop and find out what the problem is.

When you are happy that nothing is stopping the cases, ease the left case off again, keeping the shafts in the right case. Put the main case gasket in place and refit the left case. Close the case joint as far as possible by hand and gentle mallet taps on a block of hardwood over the bearing positions. All being well you should be able to close the cases before putting the bolts in and torqueing them up. Warming the left case will help I’m always reluctant to pull the cases together on the bolts, they’re easily damaged or distorted if something is stopping them. Try a few taps with the mallet before putting any serious torque on the bolts. If the cases won’t close, stop and find out why.

Well, that’s how I would go about it, hope I haven’t underestimated your intelligence. Others will have their own methods or know something that I have missed. . Please chip in.

On your other questions:-Gaskets, including the head gasket usually go in dry . I will sometimes put sealant (Hylamar) on one side of the gasket if the joint is known to weep oil. Flexible sealant (ThreeBond 1184) is used on metal to metal joints with no gasket and where bearing seats are machined across the joint( horizontally split engines). Use threadlock on the crank pinion nut and clutch centre nut. Anti seize compound (Copaslip)is helpful on the cylinder studs, before the cylinder is slid on and for the exhaust to cylinder joint nut and spark plug. Use it on threads that get really hot or where corrosion is likely to occur but not threads which have to be tightened to a specified torque.

Hope the above helps, we all have to start somewhere. I have no formal training on rebuilding engines but it is all based on practical experience and having a go. Once you’ve done the first one it gets easier. Of course, we’re all here to help if you get stuck. I am sure other members will have a better way of doing some of these operations, please feel free to add your own experience and knowledge.

I,ll help but you have to have lots of cold beer on hand and fly me to your place and i like steak with my beer should not take to long as long as the beer keeps comeing.... been doing it for 50 years one more can,t hurt....

Brian,Thanks for taking the time to write such a well thought out reply! I was hoping this thread could be used as a reference for other first time builders. If any other members have any tips or advice, please feel free to add to the discussion. Thanks again! Steve

Excellent job Brian. I am no vertical split engine guy, but for any kind of engine, (emphasizing Brian's point) dry fitting it all to be sure you have all of your parts and they are correctly oriented will save a scramble once the sealant is applied. Seems like an extra step, but this is a rule I live by and has saved me lots of heartache. Good luck Steve, and as Brian says, you just have to have a go....bert

One more thing..... back in the 70s we had made 2x4 boxes for the motors... we had a small stack of them in differnt sizes make one to fit yours... some motors you built up by layeing them on there left side.... but its been years since i did the last one..... take it slow,,, work over a big ass shop towel,,, that way when something falls.... it woun,t roll far,,,,,,, we have all been there Dam... were did it go

I'm getting ready to assemble a 100 engine that was completely taken apart before I took possession. The parts are in three different boxes. I've started cleaning various pieces and thought about sending the crank out and having the big end bearing replaced as I don't have a press. As part of their service, they will true the crank assembly once it's all reassembled.

I mentioned the crank truing only because it hadn't been brought up in this thread. I rebuilt a different engine last year that only had 563 miles on it. Because it had so few miles on it and it was is such good condition, I took the crank to a guy locally to have it checked out and he determined the big end was OK. Because the crank bearings had been pulled he decided to check the runout to make sure it was still within tolerances. Apparently all that pulling, yanking, and heating on the bearings can sometimes throw things out of alignment.